TState in ILogger interface

[alexandrehtrb]

Hello,

I am writing a custom Logger for a project and I noticed that the ILogger interface could be more straight-forward and easier to understand.

The TState generic type in the ILogger interface is vague, but in practice, it is almost (?) always an instance of the FormattedLogValues class.

runtime/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/ILogger.cs

Line 23 in 4daefae

void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter);

In LoggerExtensions.cs:

runtime/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/LoggerExtensions.cs

Line 486 in 4daefae

logger.Log(logLevel, eventId, new FormattedLogValues(message, args), exception, _messageFormatter);

ASP.NET Core logs have similar classes.

Changing the ILogger interface TState generic to concrete FormattedLogValues would make the interface clearer to understand and eliminate type checking and casting (performance benefit). In the case of ASP.NET Core, maybe it could use a derived class inheriting from FormattedLogValues.

Related issues: #90226 and #67577

[stephentoub]

The TState isn't intended for inspection. It's just to be passed through to the formatter.

[alexandrehtrb]

In my case, the Logger writes a structured log, and I need to inspect the key-value pairs from TState.